With the recent tendency toward westernized eating habits, obesity caused by hypernutrition, etc. continues to increase. Similarly, there is observed a continuous increase in obese pet animals. Namely, there arises a serious problem of obesity which is one of the risk factors for arteriosclerosis and relates also to diabetes and hypertension. Obesity means a state where fat is excessively accumulated in the body. The accumulation of fat in the body is caused by the excessive intake of saccharide (carbohydrates) or fat.
The mechanism of obesity caused by the excessive intake of carbohydrates is as follows. Carbohydrates contained in foods or beverages are digested into mono-saccharides and absorbed into the body through the small intestine. The blood sugar level thus elevated induces the secretion of insulin which acts on fat cells. As a result, the monosaccharides in the blood are incorporated into the fat cells and converted into fat.
On the other hand, fat (triglycerides) with the highest caloric content among food components is digested by pancreatic lipase and absorbed through the small intestine. Excessive calory intake brings about an increase in reserve calories. That is, the excessive fat intake results in an increase in reserve calories and, in turn, obesity.
Accordingly, studies have been made on various antiobestic agents for inhibiting some of these pathways toward obesity to thereby achieve an antiobestic effect. Namely, it is assumed that obesity can be prevented or relieved by the carbohydrase inhibitory effect, blood sugar increase inhibitory effect or monosaccharide absorption inhibitory effect, by which the pathway from the excessive intake of carbohydrates to obesity can be inhibited, or the cholic acid adsorptive excretion promoting effect, cholesterol lowering effect, blood triglyceride lowering effect or lipase inhibitory effect by which the pathway from the excessive intake of fat to obesity can be inhibited. Thus a number of studies have been carried out on drug ingredients having these effects.
First, illustration will be made of the carbohydrase inhibitory effect, monosaccharide absorption inhibitory effect and blood sugar increase inhibitory effect by which the pathway of the excessive intake of carbohydrates to obesity can be inhibited.
The term "carbohydrase" as used herein means digestive enzymes capable of degrading disaccharides (sucrose, maltose, isomaltose, lactose, trehalose, etc.) into monosaccharides (glucose, galactose, etc.) and involves .alpha.-glucosidase, .beta.-glucosidase, sucrase, maltase, isomaltase, lactase, trehalase, etc. Carbohydrase inhibitors inhibit carbohydrases capable of degrading disaccharides into monosaccharides and thus retard the digestion of orally taken carbohydrates. As a result, a rapid increase in blood sugar level after a meal is retarded. As digestion is inhibited, disaccharides are slowly degraded into monosaccharides and the absorption of the monosaccharides into the intestinal tract is retarded. Then the increase in the blood sugar is suppressed. As a result, it is assumed that the synthesis of fat from carbohydrates is suppressed and the accumu-lation of somatic fat is thus inhibited.
It is considered that a rapid increase in blood sugar level after a meal due to the excessive intake of carbohydrates (saccharides) and excessive insulin secretion caused thereby will accelerate not only obesity but also diabetes or hyperlipemia [Yakuri to Chiryo (Pharmacology and Therapy), vol. 19, NO. 10 Oct. 284 (1991)]. It is therefore assumed that diabetes or hyperlipemia can be prevented or relieved by inhibiting carbohydrases. Moreover, the prevention of hyperlipemia is an efficacious methods for preventing arteriosclerosis [Saishin Igaku Daijiten (The Newest Medical Dictionary), Ishiyaku-Shuppan, K.K., 1019 (1987)].
Accordingly, carbohydrase inhibitors, mono-saccharide absorption inhibitors or blood sugar increase inhibitors are seemingly useful as antidiabetic agents, antihyperlipemic agents or antiarteriosclerotic agents.
Carbohydrase inhibitors commercially available at the present time include Acarbose (manufactured by Bayer AG) which is an a-glucosidase inhibitor and Voglibose (manufactured by Takeda Chemical Industries, Ltd.) which is a drug for ameliorating abnormally elevated blood sugar levels arising after a meal. As a results of animal and clinical tests, it is confirmed that these drugs inhibit an increase in blood sugar level after a meal. Also, it is reported that they are efficacious against obesity and diabetes [Res. Exp. Med., vol. 175, 87 (1979); J. Japan. Agr. Chem., vol. 63, 217 (1989); and New Current, vol. 6, 2 (1995)].
Next, the cholic acid adsorptive excretion promoting effect, cholesterol lowering effect, blood triglyceride lowering effect and lipase inhibitory effect will be illustrated. These effects inhibit the pathway from fat (triglyceride) intake to obesity.
Fat (triglycerides) is degraded by pancreatic lipase and absorbed through the small intestine. It is, therefore, estimated that the inhibition of lipase results in a decrease in the blood triglyceride level and, in its turn, contributes to the prevention of obesity. By suppressing the absorption of fat through the intestinal tract, furthermore, the serum lipid level can be lowered and thus hyperlipemia can be prevented.
A cholic acid (bile acid) adsorptive excretion promoter would bind to cholic acid in the intestinal tract and increase the excretion into the feces, thus inhibiting the exogenous cholesterol absorption. To compensate for the decrease in cholic acid due to the increase in the excreted cholic acid, the catabolism of cholesterol into cholic acid is accelerated in the liver. It is estimated that the blood cholesterol level is lowered thereby. That is to say, it is considered that a cholic acid adsorptive excretion promoter is useful as an antiobestic agent, since it accelerates the catabolism of cholesterol into cholic acid and, as a result, the cholesterol is consumed and the degradation of fat, which supplies cholesterol, is promoted.
As a drug having a cholic acid adsorptive excretion promoting effect, colestyramine which is a remedy for hypercholesterolemia may be cited. It is an anion exchange resin. When orally administered, this anion exchange resin adsorbs and fixes cholic acid under enterohepatic circulation in the intestine and thus inhibits the reabsorption of cholic acid. Then the conversion of cholesterol into cholic acid is accelerated in the liver and, as a result, the blood cholesterol level is lowered. However, colestyramine should be taken in a large dose (for example, 9 g of colestyramine suspended in 100 ml of water). In addition, it has another problem that the resine has a coarse and unpleasant texture remained in the mouth, which makes ingestion unpleasant.
As discussed above, there have been reported a number of chemically synthesized compounds each having characteristic effect(s) and some of them have been already put into practical use as drugs. However, these drugs suffer from some problems such as the necessity of being administered a large dose or having an unpleasant constitution upon administration. Since these compounds are chemically synthesized, moreover, the administration thereof is sometimes accompanied by anxiety about safety. Although it is desired to add antiobestic agents to foods or beverages so as to prevent obesity, the synthetic nature of such compounds and the large dose thereof make it impossible to realize this desire. Namely, it has been desired to develop a safe antiobestic agent having a natural origin so as to satisfy the above-mentioned.
In recent years, it has been clarified that some natural substances originating in plants (for example, bark of Morus alba or hydroxycitric acid which is a component of garcinia) have blood sugar increase inhibitory effect or antiobestic activity. However, it is not appropriate to add, for example, nojirimycin which is the active ingredient of bark of Morus alba to foods or beverages, since it has an excessively strong activity. It is also reported that guava leaf extract shows inhibitory effects on maltase and sucrase [J. Japan Agr. Chem., vol. 69, 339 (1995)]. However, this substance is satisfactory neither in blood sugar increase inhibitory effect nor antiobestic activity and thus no antiobestic agent has been developed so far with the use of the same. Disclosure of the Invention
An object of the present invention is to provide a safe antiobestic agent comprising a substance originating in a natural material and having carbohydrase inhibitory effect, blood sugar increase inhibitory effect, monosaccharide absorption inhibitory effect, cholic acid adsorptive excretion promoting effect, cholesterol lowering effect, blood triglyceride lowering effect and lipase inhibitory effect.
The present inventors have conducted extensive studies to find a substance having antiobestic effect, i.e., carbohydrase inhibitory effect, blood sugar increase inhibitory effect, monosaccharide absorption inhibitory effect, cholic acid adsorptive excretion promoting effect, cholesterol lowering effect, blood triglyceride lowering effect and lipase inhibitory effect while exhibiting no harmful effect on the human body. As a result, they have found that a substance having a highly efficacious antiobestic effect is contained in tamarind seed coat extract, thus completing the present invention.